Document 6540410

DETERMINATION OF ORTHOMETRIC
HEIGHTS WITH REAL TIME
KINEMATIC SURVEYING,
KONYA SAMPLE
smail ANLIOĞ
ANLIOĞLU, Süleyman Sırrı
rrı MARA ,
Fatih UYSAL, Turkey
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CONTENT
1.
2.
3.
4.
5.
6.
INTRODUCTION
RELATIONSHIP
BETWEEN
ELLIPSOIDAL
AND
ORTHOMETRIC HEIGHTS
MULTIQUADRATIC INTERPOLATION TECHNIQUE
REAL TIME KINEMATIC TECHNIQUE AND SELECTED
REFERENCE STATION IN KONYA FOR RTK
FIELD MEASUREMENTS AND RESULTS
CONCLUSIONS
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1
INTRODUCTION
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The national geodetic networks were established separately for
horizontal and vertical control up to now. Horizontal datum is a
collection of specific points on the Earth that have been identified
according to their precise northerly or southerly locations (latitude)
and easterly or westerly locations (longitude).
Datums used in Turkey for φ, λ:
„ Turkish National Datum 1954 (ED50)
„ International Terrestrial Reference Frame (ITRF96, Ref. Epoch
1998.00)
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The vertical datum is a collection of specific points on the Earth with
known heights either above or below mean sea level. Near coastal
areas, mean sea level is determined with a tide gauge. In sea areas
away from the shore, mean sea level is determined by the shape of
the geoid. The height of any vertical control point in Turkey is
referred to the tide gauge station in Antalya.
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Datums for H (Orthometric Height):
„ Turkish National Vertical Control Network (TNVCN-99)
Datum for h (Ellipsoidal Height):
„
GRS80 ellipsoid
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Three dimensional networks
can also be established with
satellite techniques. The
Cartesian coordinates (X;Y;Z)
and the ellipsoidal coordinates
(φ, λ, h) of points are obtained
in the WGS-84. When
compared to conventional
methods, three dimensional
networks can be established
more easily, more rapidly and
more accurately by using
satellite techniques.
„In this study, the usage of geoid undulations at real time kinematic
(RTK) surveying using GPS observations is investigated. Geoid
undulations at the points in the area of interest were determined with
respect to RTK and using regional geoid model (rgm) file derived from
multi-quadratic interpolation technique. Orthometric heights known and
RTK results from study were then compared with each other.
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RELATIONSHIP BETWEEN ELLIPSOIDAL AND
ORTHOMETRIC HEIGHTS
N=hN=h-H
The geoid surface is more irregular than the ellipsoid of revolution often used
to approximate the shape of the physical Earth, but considerably smoother
than Earth's physical surface. The geometrical separation between it and the
reference ellipsoid (as GRS-80) is called as geoid undulation. The orthometric
height (H) is the distance along a line of force from a given point (P) at the
physical surface of an object to the geoid.
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Ellipsoidal height difference is determined by GPS, but
computation of geoid undulation (N) difference requires
some additional processes. The basic geoid undulation
determination techniques are:
are:
1.
2.
3.
4.
AstroAstro-geodetic method.
Geopotential models,
models,
Surface gravity techniques (i.e. Stokes' Integral),
Integral),
Geometric or interpolation methods.
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MULTIQUADRATIC INTERPOLATION TECHNIQUE
Ntrend ( x, y) = a0 + a1 y + a2 x + a3 xy + a4 y 2 + a5 xy2 + a6 x 2a7 x 2 y + a8 x 2 y 2
The multiquadratic interpolation technique was suggested by
Hardy. The purpose of this interpolation technique is to define
the best matching surface to the region of interest by a single
function using the entire control points known. It is also an
analytic solution technique. For the application of the technique,
technique,
a trend surface must be drawn. It is appropriate to use first and
second degree polynomials as a trend surface in this technique.
technique.
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n
[
N ( x , y ) = N trend + ∑ C i ( x i − x ) + ( y i − y )
i =1
2
]
1/ 2
2
n stands for the items control points, and
ci are the coefficients calculated by means of known N(x,y) values of
the control points
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REAL TIME KINEMATIC TECHNIQUE AND SELECTED
REFERENCE STATION IN KONYA FOR RTK
„
The base station re-broadcasts the
phase of the carrier that it
measured, and the mobile units
compare
their
own
phase
measurements with the ones
received from the base station.
This allows the units to calculate
their
relative
position
to
millimeters,
although
their
absolute position is accurate only
to the same accuracy as the
position of the base station.
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The typical nominal accuracy for these dual-frequency systems is
1 cm (±2ppm) horizontally and 2 cm (±2ppm) vertically. Also these
values may change according to capabilities of GPS receiver,
communication, distance between base receiver and the rover receiver,
distance-dependent biases (orbit bias), ionosphere and troposphere
bias.
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„
Konya Municipality started to operate single reference station for RTK
positioning, whereby users can receive the corrections within the
municipality boundary. Topcon NET G3 reference station receiver was
employed. This reference station is controlled by a central server. TopNET
7.12 Reference Station software is used for data processing.
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FIELD MEASUREMENTS AND RESULTS
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Field works were done according to big scale map and map information
production regulations for Konya metropolitan city, in autumn 2007.
6 Turkish National Fundamental GPS Network (TUTGA) points,
8 stations graded as C1
24 stations graded as C2
1218 stations graded as C3
Total area is approximately 1800 km2
4 Leica System 1200 receivers and 4 Javad GPS receivers and their antennas
Observations with 10" interval within 30-minute period, totally for 1369 points
The measurements were completed in 25 days in May and June 2007
Pinnacle 1.0 for processing and adjusting
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„
Geometric Levelling
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3 Topcon DL-101C, Topcon DL-102C and Sokkisha SDL30
Measurements completed in 5 months between April and July 2007
The geometric leveling network has 2843 height difference and
1885 stations
6 points whose coordinates were known in Turkish National Vertical
Control Network (TNVCN-99)
Root mean square (rms) of leveling adjustment is ±7.56 mm
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The second order-nine parameter multi-quadratic surface was fitted
to the topography by using well distributed 1175 control points.
„
rms of surface is ± 4.5 cm
N = a1 + a 2 y + a 3 x + a 4 y 2 + a 5 xy 2 + a 6 xy + a 7 x 2 + a8 x 2 y + a 9 x 2 y 2
Coefficients of multi-quadratic surface equation
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a1
a2
a3
a4
a5
a6
a7
a8
a9
=
=
=
=
=
=
=
=
=
35.848719452232800
-0.000006229550258
0.000005929540559
0.000000000004456
-0.000000000000024
-0.000000000230247
-0.000000000108540
0.000000000000025
0.000000000000000
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Geoid undulations of 30’’x30’’
spacing grid points were
computed from coefficients of
multi-quadratic surface to use
in regional geoid model file
(*.rgm) for Topcon RTK GPS
receivers.
LAT,LON, n_row, n_column,
step_lat,step_lon, geoid_direction, ellipsoid;
37 43 30, 32 21 00, 45, 50,
00 30, 00 30, NE, GRS80;
H1 H2 H3
35.807 35.815 35.823
H4 H5 H6
35.785 35.795 35.805
H7 H8 H9
35.764 35.776 35.788
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The orthometric heights of 34
points obtained by Topcon GR3
double frequency receiver have
been compared with original
heights in the chosen test area.
Occupation time 9 seconds
29 points were used for the
orthometric height testing, rms of
5 points >3σ
Accuracy ± l.8 cm in easting, ± 2
cm in northing using RTK
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The height difference between the highest and lowest points in
the test area was approximately 377.4 meters.
The height differences were in the range of ± 18 cm
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There are no systematic errors in ellipsoidal height
determination by GPS. The difference between orthometric
heights estimated by leveling adjustment and the ones
obtained by RTK with geoid model (the geoid model + GPS
ellipsoidal heights) can be attributed to
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random noise in the values of h, H, N in Konya Vertical Control network
Datum inconsistencies and other possible systematic distortions in the
three height data sets (e.g. long-wavelength systematic errors in N,
distortions in the vertical datum due to an over constrained adjustment of
the leveling network, deviation between gravimetric geoid and reference
surface of the leveling datum).
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CONCLUSIONS
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The feasibility of determining real-time orthometric heights by RTK at
the cm-level accuracy is shown in Konya sample.
The RTK GPS survey technique may be an efficient and accurate
alternative to the leveling techniques currently being used.
On average, the results agree to within 10 cm. The regional geoid
model was estimated from second degree multi-quadratic surface in
this study.
According to ellipsoidal heights, the deviations of orthometric heights
are twofold. The estimated surface may be incompatible with
topography.
However, further tests on the larger network with a greater number of
stations may provide more insight to RTK with geoid model method as
an alternative to leveling.
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THANK YOU FOR LISTENING
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